you were asked to calculate the concentration of a bacterial culture Part I 1-.
ID: 281196 • Letter: Y
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you were asked to calculate the concentration of a bacterial culture Part I 1-. You were asked to calculate the concentration of a bacterial cuture. To complete the task you made the next serial dilution sequence: l/100 ? 1/2?1/5?1/10 From the last dilution you loaded in the hemocytometer and counted four 0.00000625 mm3 squares Square Bacterial count 132 140 150 110 Calculate: a) Hemocytomter factor b) Accumulated dilution ( Inverse of the accumulated dilution factor) c) Average of bacterium in each square d) CFU of the culture 2 - You were asked to make a series of dilutions to calculate the viable CFU/ml of a bacterial culture. You made the next serial dilution before plating the culture Original culture 1/100 1/4-1/3-1/10 From the last dilution you plated one tenth of the volume. After incubating for 24h at 37C 120 colonies grew on the plate Calculate the CFU/ml of the original cultureExplanation / Answer
Q1; a) The heamocytometer factor is simply the volume of the small square of the haemocytometer. In this case it is 0.00000625 mm3 or 6.25 x 10 -9 mL.
b) The sample was diluted 100 times (1/100). After that it was again diluted by 1/2 ( 1/200 times dilution) and gain by 1/5 ( 1/1000 times dilution). Finally the sample was diluted by 1/10 ( 1/10000 times dilution).
Hence the original sample was diluted 10000 times.
c) The average of bacteria in each squre can be calculated by using
Avg. bacteria in each square = No. of cells in each square x dilution factor / Vol. of small square (mL)
d) Assuming that each bactrial cell gives rise to a colony on a petri dish, (CFU) the CFU/mL is the number of cells in each square.
Q: It can also be done as above.
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